Method for preventing scorification of fire bars, grate surfaces, and the like



Patented Mar. 27, 1928.

UNITED STATES 1,663,944 PATENT OFFICE.

ROBERT HOPFELT, OF HAMBURG, GERMANY, ASSIGNDR TO THE FIRM METALLISATOR I BERLIN AK'IIEN-GESELLSCHAFT,=OF BERLIN-NEUKOLLN, GERMANY.

METHOD FOR PREVENTING SCORIFICATION OF FIRE BARS, GRATE SURFACES, AND

' THE LIKE.

No Drawing. Application filed January 29, 1925, Serial No. 5,661, and in Germany partly on February 28,

. It is known to prevent scorification of, or formation of slag on, grate-surfaces, the or furnace-bars and the like, while at the same time increasing the fire proof quality of the metal, by providing it with a layer of aluminium on such places as are subjected to the action of heat and the influence of slag. This layer is produced by projecting divided aluminium in a molten state against the surface to be coated, and thereupon slowly heating the work piece to a temperature approximating the melting temperature of the metal of the work piece. The idea was that bythe subsequent heating of the work piece thus besprinkled with aluminium an alloying between the aluminium and the ground metal takes place. This, however, is an erroneous conclusion. The aluminium which has been applied to the work iece' in a cold state is very porous, and since aluminium easily oxidizes, this porous aluminlum layer in the subsequent treatment eagerly takes up oxygen and is thus turned into aluminic oxide which for itself adheres only loosely to the thus coated article. When such a coated and heated work pieceis cooled 'down the coating generally scales off quickly, the more so when the work piece is subjected to mechanical treatment while in the fire, particularly by pokers, rakes or stoke bars.

It has been moreover proposed to produce an alloying of the metal coating wit-h'the ground meta-l by subsequently heating the besprinkled work piece 1n an inert aseous atmosphere, consisting for instance 0 nitrogen or hydrogen. Even such method falls with aluminium not to speak of the fact that it is extremely costly and complicated and requires exceptionally precautious measures. The substance of the present invention is a method which allows fire bars or the like to be provided with an aluminium coating in such manner that it adheres extraordinarily firmly by intimately alloying with the ground metal, and besides makes the surface of the work piece so hard that it withstands all thermic and mechanical treatment much better than all heretofore known fire-bars, no matter how the composition is effected.

The invention is'based on the discovery that aluminium adheres-with absolute certainty, for instance to an iron work piece, when the latter is heated previously to "a temperature in which the aluminium melts.

The preheating of a work piece to be besprinkled is in itself known. However, for the present object this measure of-preheating the work piece is not sufficient. Care must be taken, that, when it is desired to attain the object of the present invention, the surface of the work piece while being preheated does not oxidize, because only with such precautions does a flowing together of the aluminium projected on the heated workpiece, with the ground metal of the workpiece, takes place. Theoretically such oxidation could be prevented even, it is true, in such way as is known by allowing the preheating of the work piece to take place in an indifferent gaseous atmosphere.

Practically, however, it is either impossible tohave recourse .to this way or only possible with extraordinary difliculties, because aside rom the 'difliculties spoken of above in'connection with the use of an indifferent gaseous atmosphere it would be necessary to take care that the projecting of the aluminium should also take place within this atmosphere, and even before the work piece comes in contact with air whereby it would be oxidized.

The invention follows therefore a quite diiferent course; according to which a thin aluminium layer is projected on the work piece in a cold state, which layer should be just so thickthat the surface of the work piece is protected against oxidation. The

work piece thus provisionally coatedv is heated up to about 800 C. that is to say to a temperature which'is approximately the melting point of the aluminium. When on such heating the provisional layer of aluminium is turned partly into aluminic oxide this will. notbe-of any harm, because this aluminic oxide layer fulfills its purpose to'protect the ground metal against oxidation, it not being acted upon mechanically...

When now in this heated state of the work piece another aluminium layer is projected upon the previously applied coating to the required thickness, this aluminium layer combines intimately with the ground metal because theprovisionallyprojected porous and thin aluminium layer will be penetrated by the particles of the finally projected aluminium layer which casts aside any oxides that might have been created by the provisional aluminium-layer, and such oxides would be made harmless by being encased or reduced.

, piece to 1000 C. and more.

V heating, which when it is carried out sufli ly combined with the When thus the final aluminium layer is applied by projeetion to'the sufiicient thickness, now the known subsequent treatment-can take place by againheating or again raising the temperature of the besprinkled work Since then an intimate reciprocal contact ofthe ground metal and the projected aluminium has taken place an even alloying ofthe two metals over the complete area results, and in this manner alloys of almost any composition between the ground metal and the aluminium can be carried out, by appro' riate choice of the amount of the ,projecte aluminium and of the temperatures in the subsequent treatment.

Under certain circumstances the subsequentheating' may be omitted, that is to say when the work piece durin the ordinary treatment has been subjecte to sufllcient oiently long, need not arrive at-1000 C.

c When the work to the new method deseribed aboveare ex amined by the microscope, it will be found that the aluminium layer has been intimatecomplete surface to orm an allo However, the adhering is not'so complete on certain places of the surface of the' work iece if this consists of cast-iron.' Thereore' it can be concluded that cast iron work pieces have spots or places in which free carn is present to a greater amount, {which prevents the formation of alloy, and thereore an unevenness in the adhering of the coating results. l

Starting from this discovery according to a further feature of the invention the work pieces,'as far as they contain larger amounts of carbon, will be superficially freed fromsuch carbon in. an atmosphere, which-is preferablv not oxidizable', and which comprises constituents which withcarb'on are turned into a gaseous combination or which consists of such. In the first instance for such'atmosphere hydrogen is well adapted, particillarly in the form of illuminating or burnmg the creation of b pieces treated accordingground metal over the if theground metal is steel or wrong t iron.

tion subsequent quantit gas, which combines with carbon to' form hydrocarbon. Also nitrogen is applicable since it forms cyanogen as or ammonia. It is suflicient if the sur ace only is decarbonized, since only this is to alloy with the coatin The annealing of the work piece can take place either in a state when not yet besprinkled or eventually then when the first thin aluminium layer'has been applied. In the latter case the annealing must be very exactly regulated and care must be taken, to increase the temperature only slowly, so as not to prevent a timely harmless escape of the gaseous carbon comb ing of the still rous coating, and thus i'sters and scaling off of the second final coating is prevented. The annealing, after the first coating has been applied, has the advantage that it can be combined with the heating of the article up to the melting temperature of aluminium, which in any case is necessary as the first operation.

.It may be still further remarked that the superficial decarbonizing of work pieces, which are tobe tinned or zinced by the aid of bodies which giveofi oxygen in the heat, is known. -\From this known method the asmuch as the annealing for the purpose of superficial decarbonization takes 'placein a non-oxidizing atmosphere.

I claim:

A method for preventing the seorification of fire or furnace 'bars, grates and the like comprising projecting molten aluminium against the cold work-piece to form upon it a preliminary firml adherent coating, heating the'coated worlipiece to approximately the fusion temperiiture of the aluminium, thereby alloying the inner portion of said coating with the workpiece, the'outer porbecoming oxidized of molten aluminium against said coa workpiece while still in its heated state, therebybreaking. through the layer of oxide, and forming an, integral accretion to the inner ducing a coatingiof any desired thickness.

OBERT J. ,HOPFELT.

and projecting a 7 alloyed portion, pro 

